In a wireless communication system, a transmitter modulates data onto a radio frequency (RF) carrier signal to generate an RF modulated signal that is more suitable for transmission. The transmitter then transmits the RF modulated signal via a wireless channel to a receiver. The transmitted signal may reach the receiver via one or more propagation paths (e.g., a line-of-sight path and/or reflected paths). The characteristics of the propagation paths may vary over time due to various phenomena such as fading and multipath. Consequently, the transmitted signal may experience different channel conditions and may be received with different amplitudes and/or phases over time.
To provide diversity against deleterious path effects, multiple antennas may be used to receive the RF modulated signal. At least one propagation path typically exists between the transmit antenna and each of the receive antennas. If the propagation paths for different receive antennas are independent, which is generally true to at least an extent, then diversity increases and the received signal quality improves when multiple antennas are used to receive the RF modulated signal.
A multi-antenna receiver conventionally has one RF receiver processing path (or simply, “receive path”) for each frequency band and each receive antenna. For example, if the multi-antenna receiver is designed to operate at two frequency bands (e.g., cellular and PCS bands), then it would normally have four receive paths for the two frequency bands for each of the two receive antennas. Each receive path includes various circuit blocks (e.g., amplifiers, filters, mixers, and so on) used to condition and process a received signal at a designated frequency band from an associated antenna. The circuit blocks are typically designed to meet various system requirements such as linearity, dynamic range, sensitivity, out-of-band rejection, and so on, as is known in the art. In conventional receiver designs, the receive path is often replicated for each frequency band of each of the receive antennas, with circuit modifications (as needed) for different frequency bands. The replication of the receive path circuitry results in higher cost, larger area, and higher power consumption for the multi-antenna receiver, all of which are undesirable. There is therefore a need in the art for a low-cost diversity receiver.